1. Field of the Invention
The present invention pertains to swivel devices for rotatably supporting loads. More particularly, the present invention pertains to apparatus for supporting and permitting rotation of a liner pipe string in a well during the process of cementing the liner pipe string in place.
2. Description of Prior Art
A liner is a section of casing or tubing which is suspended in a well without normally extending to the surface. Two or more such sections constitute a liner string. Cemented liners are utilized for a number of reasons: providing well control, reducing initial cost of casing, more rapid installation than of full casing strings, etc. Liners may be installed entirely within outer casing strings or partially in an open hole.
Conventionally, a liner is set and cemented by first lowering the liner supported by a liner hanger and a setting tool, which is connected to an operating string, into the well bore. The liner is hung, usually on slips, and the setting tool is released from the hanger. Cement is then pumped through the operating string into the liner, and displaced from the liner, usually through a foot valve, into the annular space between the liner and the surrounding casing or well bore. The details of such a cementing operation, as well as various tools for carrying it out, are well known in the prior art.
It has been found, especially where the liner string to be cemented is of considerable length, that the cement will more easily circulate down the liner string and up the annular region between the liner string and the well casing or bore if, during the cementing operation, the liner string is rotated. Such a rotation of the liner pipe string requires rotational motion of the liner with respect to the liner hanger, which is fixed with respect to the well casing above the liner pipe string by the hanger slips. Consequently, in such a case, the liner pipe string must be supported by the liner hanger through some sort of a rotatable coupling device. Such rotatable coupling devices with mechanical bearings are well known in the art. Typical rotating liner hangers employed in the oil and gas industry feature ball bearing assemblies to carry the load of the liner pipe string and permit rotational motion between the liner string and the hanger slips. However, mechanical bearing devices used in this manner are susceptible to undesirable unequal loading. This is particularly true where the well bore is not straight, or is not exactly vertical. Unequal loading also occurs where two or more mechanical bearing assemblies are stacked vertically in the liner hanger.